Concept:The hard, unweathered rock layer cannot be penetrated by tree roots and therefore cannot support their growth.
Explanation:Horizon A is the topsoil, rich in humus and nutrients, so it provides a good medium for roots.
Horizon B is the subsoil, where tree roots can extend to absorb water and minerals.
Horizon C is the weathered parent material, which still allows some root penetration.
Horizon D is the bedrock, a hard and massive layer of rock.
Since tree crop roots cannot break through this solid rock to obtain anchorage and nutrients, Horizon D does not support the growth of tree crops.
Answer:Horizon D
